Thanks for that Earl. I also tried the splash tweeters and found them to be OK. I usually ended up playing them straight ahead, tho, out of guilt or embarrassment something.

I suspect that different people hear things differently. I don't get much, if any, spacial benefit from tweeters, more of a tonality benefit. Like warmth on strings.

These Fostex are bullet type tweeters so I feel it's necessary to point them away from me ( no matter what! ).

I do agree that the tweeter "splash" detracts some from the "front-to-back" imaging ( if that is what you implied ).
- Keeping that in mind I'll be working to reduce the tweeters measurable effects ( from say 5K to 10K ).

Here's an REW wavelet showing the relative strength of this tweeter ( relating to the Altec 802 ) and it's shortish time signature/echo ( it's only 18" from the back wall ) .

One thing I'll say is that this is the first time one of these Fostex has remained hooked up longer than 15 minutes ( now, going on about 7 days > so that's a record ).

My experience with oldskool drivers is limited, but experiments by other diy-ers have shown these often don't go well with waveguides.
For this reason it's quite surprising the Faital Pro's appear to be an exception, as they have a conical adaptation horn. I suspect the phase-plug design is a key factor here.

Addition:
The shape (length and flare-rate) of the conical exit part also plays a role.

The DDS is certainly not bad, the slightly rough top octave is probably caused by anomalies at the throat.

The original QSC 152i waveguide was designed to work with Celestion drivers. Your measurements confirm it.
The main difference between the Celestion CDX1-1747 and the CDX1-1745 is in the suspension/damping of the diaphragm.

I think I have a pair of horns like that, bought on close-out from Parts Express. I was going to use them the Peerless compression drivers, but never got around to it. Still sitting on a shelf somewhere. Nice to see measurements with other drivers.